Oral care compositions, including toothpaste compositions, can contain fluoride salts, abrasives, and flavors to clean teeth, freshen breath, and maintain the aesthetics and health of the oral cavity, including the teeth and gums. It can also be desirable to include potassium nitrate (KNO3) in oral care compositions to help reduce pain from sensitive teeth (dentinal hypersensitivity).
Formulating toothpaste compositions with the proper rheology can be very challenging. The composition must not be too thick so it can easily dispense out of a tube but thick enough to stand up on a toothbrush without sinking into the bristles. The viscosity of the oral composition must remain stable over time as not to continue to thicken so the oral composition remains easy to dispense during the shelf life. Once dispensed from a container, the oral composition should not be stringy or sticky as to be messy for a consumer to use. The oral composition must also easily disperse once in the mouth and foam. It is also desired that the oral composition not stick to a sink or leave difficult to remove residue. In addition to balancing the viscosity and shear thinning to formulate acceptable rheology, the oral composition must also keep active ingredients including fluoride salts and potassium nitrate stable and available.
One way to improve toothpaste rheology and stability is to include a gel network phase as a structurant. The gel network phase can include a fatty amphiphile, such as a fatty alcohol, and a secondary surfactant. Including a gel network phase can also provide a unique brushing experience. For instance, toothpaste that contains a gel network phase can have excellent foaming and the foam may not easily break down during brushing, even when it is used with an electric toothbrush. Also, some commercially available toothpastes can feel harsh and can irritate a user's mouth, however, toothpastes containing gel networks can feel smooth and are generally non-irritating. Additionally, after brushing, the mouth not only feels fresh and clean, but a user's teeth can feel especially smooth and the smoothness can persist throughout the day because the amount of biofilm that builds on the teeth between brushings can be significantly reduced.
However, it can be particularly difficult to formulate stable toothpaste compositions with a gel network phase that also contains an effective level of a salt, such as KNO3. For instance, unacceptable phase separation has been observed in toothpastes that contain a gel network phase and KNO3.
As such, there is a need for an improved oral care composition that has an effective level of a salt, such as KNO3, and sufficient rheology and where the phases are stable.